Can Energy-Efficient Framing Handle High Winds?

The release of a new draft specification for the EPA's
Energy Star 2011, guidelines for Energy Star qualified new
homes program, has raised concerns among some energy raters and
builders about whether advanced energy-efficient framing techniques
required by the program are compatible with the beefy framing
details needed to handle lateral pressures of wind in coastal
regions.
The new spec, slated to take effect in 2011, includes a new
"Framing
Checklist" that calls for two-stud corners, two-foot on-center
stud spacing, single-member window and door headers, and framing
reductions at window and door openings. The official comment period
on the initial draft version ended this summer, and EPA officials
are now working on a revised final version. Meanwhile,
comments on the draft have been collected and are published on
the EPA's website. Michael Watt, Executive V.P. of the Long Island
Builders Institute, made note of the potential structural conflicts
in his comment, observing, "some Long Island [New York]
municipalities will not allow items 2.1.1, 2.1.3, or 2.2 [two-stud
corners, reduced framing around windows, and insulated sheathing].
The wind loads we are required to design to do not allow these
practices."

A 2002 DOE "Technology Fact Sheet"shows advanced framing details like those being proposed in the
Energy Star 2011 guidelines. Feedback from the construction
community raised questions about whether the guidelines would meet
code and whether reduced framing at large openings could withstand
hurricane-force wind loads.
Alabama-based architect Sue Coleman, of Sun Plans, Inc., opposed
the new framing checklist, arguing, "Framing is often determined by
structural engineers with building inspector oversight. Some high
wind areas and the Fortified Building Program which promotes
building above code wind minimums do not allow for advanced
framing."
But engineer Tim Reinhold, P.E., the Director of Engineering and
V.P. of the Institute
for Building and Home Safety (IBHS), which developed the
"Fortified ... for safer living" above-code construction program,
says that two-foot on-center spacing and other "value engineered"
framing techniques won't necessarily conflict with that standard.
"In terms of hold-downs, there are some issues," says Reinhold,
"because some of the big hold-downs that you end up with in coastal
areas, you need to have double studs, in order to be able to anchor
to it and distribute that load up into the shearwall. But the
spacing of the interior members has no bearing on the shear
capacity." Studs that fall in between panel joints, in other words,
do not factor into the racking resistance of a framed wall: "It's
really dependent on the perimeter framing," says Reinhold.
"You may have to go to a bigger stud — a 2x6 instead of a
2x4," says Reinhold. "But then that gives you room for more
insulation too, which increases your energy efficiency. And then
the idea is that you line up the studs with the roof rafters (stack
framing), so that you by-pass the top plate — which is why
you can go with a single top plate."
On the other hand, Washington State University engineering
professor Dan Dolan points out, shear capacity or racking
resistance isn't the only wind issue wall frames have to deal with.
There are also "out-of-plane" forces — that is, the pressure
of wind directly against a framed wall, which acts to bend the wall
studs or to push in windows and doors.
Dolan has been one of the leading participants in building code
committee work on wall bracing revisions for the International
Residential Code (IRC). Reducing the number of studs in a wall
segment between panel joints has "no effect on the response in the
shearwall. None. But it has a big effect on the out-of-plane
loading on that wall," Dolan explains. The issue is highly
significant for framing of large openings in the wall, he goes on:
"If you look at somewhere like Phoenix, Arizona, they can hardly
get by without something like four king studs around a double-wide
garage door, because the wind load coming in there becomes so high.
And Phoenix is not like a hurricane zone. But they can’t get
the thing to stand up. That's why when you start saying, 'We're
going to take out these jack studs and king studs,' I say, 'Whoa,
wait a minute.'"
"Consider a double sliding glass door going out onto a deck,"
says Dolan. "All that load from that door comes into the king posts
on the side of it. Even if it goes up to the header first, and then
comes across, those studs at the edge of the opening become pretty
heavily loaded in some not very high wind load zones. It really
depends on the configuration of the wall. If you have little
double-hung windows, you don’t have a problem, usually. But
when you start getting big walls of glass into the building, you
got big problems. More than just energy — you got structural
problems, quick."
Real-World Details

In coastal Florida, brothers Scott Murray (a former builder) and
Brian Murray (an engineer) have been working recently on the
intersection between energy-efficiency issues and wind-resistant
structural issues. " I used to be a builder for a larger company
years ago," says Scott Murray, "and I partnered with Brian to work
with him on his designs. We do a lot of up-front master plan design
with production and semi-production builders that have been looking
into advanced framing, and when we first looked at it, we thought
it would not work, the way we currently design and the way things
are being framed. But when I was looking to build my personal
house, and we took a closer look, we found that 2-foot on-center
spacing and single top plates and single-ply headers will work in
this area [the 120-mph wind speed zone near St. Augustine,
Florida]. I think the higher wind speeds, there obviously are going
to be more limitations. But for the 120-mph wind speed, we are able
to make a majority of those components work in some
circumstances."
"It does depend on the geometry of the house, its location, and
the exposure," Murray notes. "For some of the big builders we work
with, their homes typically are sometimes a little bit more cut up,
where a lot of this stuff is just not architecturally laid out
properly to take full advantage of efficient framing. So they are
starting to see now where they have to start up from scratch, not
just start with the engineering portion, if they want to take full
benefit."
In the real world of house framing, however, the devil is in the
details. For Scott Murray's own house — which APA - The
Engineered Wood Association has been publicizing as an example of
advanced framing methods and raised-floor, conditioned-crawlspace
construction — Murray elected to use a double top plate
simply because pre-cut studs were not available in his market at
the right length to use with a single plate. "We didn't want the
framer to have to cut every stud to length so that the drywall
would work," says Murray.
And when the time came to frame walls, the Murrays decided to
use double studs at every vertical panel joint also. "Looking at
it," says Scott Murray, "we could have eliminated that stud. And
the wall was designed with studs two feet on center. But when the
framer got to the site, he was extremely concerned about getting
the amount of nails into those perimeter studs that we were calling
out. Some of these panels along a wall segment may need nails at
three inches on center — they get that tight. And we were
concerned about the amount of nails for each panel going into that
one stud at a panel break."
"You know, it's humanly applied," says Murray. "And that is the
main system that resists both uplift and shear — there is no
redundancy in it, the nail has to be shot just perfectly into the
stud. There was concern there, and the framer had allocated for
enough material to run studs 16 inches on center. And we were
concerned also, so they double-studded it up."

The doubled studs used here at panel
seamsdefeat the energy-efficient framing scheme,
but the framer worried that the large number of 3-inch on-center
fasteners would splinter a single stud.

When even professional engineers and builders struggle with the
practical issues of combining energy-efficient building science
with wood-frame structural engineering, it's no wonder that energy
raters, who may have little if any structural knowledge or framing
experience, balk at the idea of interfering with framing decisions.
In Florida, however, there is strong pressure now to solve the
puzzle and find answers — and not just because of the
voluntary Energy Star program. C. W. Macomber, an APA field
engineer based in Florida and specializing in wind-resistant
construction for the Southeast region, says, "In Florida, our
governor has set a mandate for homes to be 50% more
energy-efficient by the year 2018. To do that, builders are
starting to see that they have to take advantage of every chance to
squeeze out more energy savings from their systems, wherever they
can."